Electronics Repair Questions & Answers 21

HI Boling,

My goal for this year is only to bring in more customers to be realistic.

Good to know about that. Without customers there will be nothing happen. For your information i have just asked my partner to check on the local newspaper rate to advertise on the repair courses.

This monitor is 15″ GTC (local brand) and was made in the year of about 1999 ( not written ). When I was using my pattern generator to check its display, I unintentionally tested it with resolution which is higher than the monitor can handle and the display went black ( nothing displayed ) without any remark like display not supported, etc. Because pressing down further the generator button will give higher resolution. Now the monitor will only display in the lowest resolution 640×480, test it with higher resolution become blank, before it was OK until 800×600 dpi.

What component could be bad with increasing the resolution unintentionally beyond the monitor can handle?

Try direct replace the h/v oscillator and make sure the s-correction circuit do not have bad fet and non polar cap.

Is there any way to increase the resolution of an old CRT monitor?

The resolution is already set and designed that way thus i do not think it can be modified to run on higher resolution.

Jestine

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Hello Jestine.

I’ve now got a 20″ LCD TV open. I replaced all caps but 4 of them which are supposed to be 470×25. No room to fit the

regular size ones in because of 2 heatsinks close to each

other. Is it possable to use 220×25 volt capacitors in their

place and they actualy fit in there and are the right size.

Gary

Hi Gary,

220uf seems to be too low and if it work now and I’m sure it won’t last long. Perhaps you need to modify or to add longer wire and secure the caps with cable tie.

Jestine
http://www.JestineYong.com

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I Have been working on computers for a few years and thought that lcd tv’s would be the same as lcd monitors and I have no problem identifying and repairing bad capacitors. However I have a Dell W2600 LCD tv that will not power up. after a little research I have found that memory chip I232 on the main board is the problem. If I freeze it with spray I can turn the tv on, but as soon as you turn it off it will not come back on unless you freeze it again. Any suggestions or help on if the chip can be change by a do it yourself-er ? Thanks

HI Robert,

Thanks for the photo and it seems to be a smaller type of BGA IC . This is not an ordinary chip and you may use a BGA machine to extract it out. But before that you need to find if there are any company selling this part or not. Or you can try modify a small fan blowing to the ic and see if it will still turn off or not.

Jestine

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Hi Dr,

I have Engine Control Unite ( Toyota Denso ) broken so I fine three capacitors :
1-       225 K2A
n

2-        472
C50
n

I did not find then in market so Can I put a capacitor from other type and have about same capacitance ?

Question :
is there are a prolem if I replace Metal polyster capacitor with any diferet type ?

You can try to test it because in some sentitive circuit they only require back the same type of capacitors.

Jestine

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Hi
thanks for ur reply its not that  its just rf input when i plug into it, it just says nothing a blank screen and when av cables are plugged in through dvd or set top box its working.

Ramachary

Hi Rama,

If you run from the dvd and have picture but no picture when plug in the rf then suspect the tuner or no supply voltage to the tuner. i guess you may need to check on the supply voltage first before replacing the tuner.

Jestine

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Dear Mr Jestine,

I would appreciate your opinion on this tester.

http://www.polarinstruments.com/products/toneohm/toneohm950.html

Thanks

Ehsan

Hi Ehsan,

I have heard about this tester many years back but i personally have not use it thus i can’t give and y advice on this matter. It has some similar features with EDS Leakseeker 82B which is to locate shorted components in high density board.

Jestine

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Hi

 

I’m now learning to repair electronics and wondering if it is possible to check a certain IC amplifier out of circuit?

The part number is TA7137P

Thanks for any input on this.

John

Hi John,

To check any ic the best is to power up the ic and measure the input/output waveform with scope. Before that you need to download the spec of the ic.

Jestine

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Hi Jestine

I tested the batteries each battery by it self, not under a load each tests at 13.0 volts do you have any suggestion on how to check if the batteries are weak like under a load?

Jeff

HI Jeff,

A bad battery can be tested good using normal type of multimeter. Here i use the car battery tester to test the UPS battery which is much more accurate. If the battery is weak the 12 volt (tested good with multimeter) will immediately go down to few volts. Try go to your favorite car mechanic and just lend it to test those batteries so that you do not need to buy one.

Jestine

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HI George,

Is it okay to modify my esr meter? i want to lengthen the test probe, is there any effect will happened in the tester if any? can i replace it with the long one?

Yes you can but the test leads cannot be longer than 30cm.

another thing is can i ask you a link or info on how to know the pin out of the plyback?

http://electronicrepairguide.com/flyback-transformer-pinout.html

http://electronicrepairguide.com/flyback-transformer-abl-pin.html

Jestine

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Hi, Jestine
I really enjoy the repair tip article, I do LCD TV repair work only
as a hobby and really enjoy it, but I would like to ask you
what kind of soldering station would you recommend
for soldering circuit boards there are so any out there figured
I would ask someone that has live there life with a soldering iron
in there hand. thanks for any help you can give me.

HI Mike,

The one that I’m using is hakko 981 dual mode solder gun. I do not have soldering station but I’ve heard that the below link soldering station is good:

http://www.brighttechnologies.in/product-images/33-Weller%20Soldering%20Tips-Large.jpg

Jestine

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Hi Sir Justin,

Good Day!

Belated Merry Christmas and Happy New to you and your family!!!

sir i just want to ask about LCD Monitors, my boss got a touchscreen LCD Monitor for Photo processing computer, the function of the computer is just save all the client picture in different format, but lately my personnel in his photo processing store complaint in me about the monitor of the said computer. they said that it is flickering even in no signal. i tried replace the lcd monitor with other working lcd monitor with a touch built into it. the original got touchscreen sensor.  after i changed the lcd with touch screen sensor with the new one without touch screen sensor.  the display is just fine… no flicking happen even in no signal.  i open the lcd and look for any bad component sign, like bulky caps, but i found nothing.  the supply of the lcd is 12 volts. directly connected to display bord. in the display bord there is 2 e-caps, i tried changing the e-caps but still the same. im sure the videocard is ok because if i change the lcd with different lcd it work fine.

my question is:   what is the most common problem with the lcd why it is flickering?  where or what stage of the lcd should i check? pls help me sir.

thanks you so much.

HI Gil,

If all the output voltages from the power supply are good and stable then one of the backlight could have problem. A weak backlight will cause flickering symptom.

Jestine

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We have here Super General LCD TV.. Upon switched ON it works and after 1 hour or two hours it appears like shaking pictures with black dim and upon turning OFF then switch ON again it appears ok picture.. then in a few minutes it will shakin pictures again.. Any pin pointed parts to be check?

Thank you if you could give some points!

Rodskie

HI Rodskie,

It could be bad filter caps in the output section of power supply or you may need a coolant to detect where the fault is by spraying on the mainboard, inverter or the t-con board.

Jestine

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HI Brad,

I am just a novice at this but I was thinking the problem to be more likely a leaky transistor on the the blue electron gun driver circuit due to the exclusive blue lines showing up on the screen. Is this possible/probable ?

One horizontal line usually is the vertical area problem. You can try checking the blue circuit components by comparing the green and the red circuit.

One last thing, if I open the crt up and discharge the anode properly with a tool to the frame ground, should I need to discharge anything else for it to be safe to work in the monitor ? i.e. capacitators, etc. will it be safe to touch all the boards after I discharge the anode and of course the monitor is not connected to power in wall ?

You need to discharge the big fat capacitor in the power primary side too. Once these tho components discharged you can safely work on the board.

Jestine

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plz confirm the printer error 41.3 for hp colour lj 4345 printer

If all the wiring and connectors are good then the problem is in laser scanner assemblies.

Jestine

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HI Chris,

Need your help in identifying a transistor, can’t seem to find the specific data sheet ( i.e., All Data Sheets or Data Sheet Catalog) for it, maybe you can find

it in your semiconductor book.  It is small, has squareish case (like a C1740,

same size), and the only number on it is  ‘ 1209 ‘, with  ‘ 4A ‘ below this. It has

three leads, and my DMM measures open between middle and outer leads,

even with meter leads reversed, and about  63K ohms between the outer leads,

again even with meter leads reversed.  Is this a Darlington, or a FET ?  It is

from the Daytime Running Lamps module in my car;  the other components

test OK.  It was made by Imasen in Japan, wrote them an email a month

ago, nobody answers (also wrote NTE two months ago, still no answer).  Just need to identify this transistor, and know whether or not it’s good or bad, so I can get the module fixed.

Thanx loads for your help !

I guess you are looking for this transistor:

http://www.datasheetarchive.com/KSR1209-datasheet.html

You can download the pdf by clicking on the pdf logo on the left in the website. Since this resistor has a built in bias resistor thus you need another good one to compare the result.

Hope this helps!

Jestine
http://www.JestineYong.com

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Jestine,

 

I am an electrical/computer engineer, and sometimes fix electronics for fun. This weekend I got a broken TV from CraigsList, its a Westinghouse w4207. I downloaded a book suggested by Dave at GrantPass repairs (saw him on youtube) and understood a thing or two about SMPS. However, in this case, all the caps look fine, and the SMPS outputs 24 volts to the inverter board. When you turn on the TV, the master board comes on, then the slave board, but that shuts off immediately followed by the master board. I have checked the mosfets on either board and the transformers with a DMM, and they look good as far as I can tell. I haven’t been able to visually check the CCFLs because they seem to be hard to get to. So my question to you is, have you come across this model before. (I think this panel is also used in view logic and the In v board is made by LG Philips — 6632L-0327A.). Please let me know if you have any suggestions on what to do next. ( have already ordered a slave board from ebay– it was only 20 bucks. and slightly different– 6632L-0327B)

Binto

HI Binto,

I have not repair any of the Westinghouse LCD TV before but most of the brand in the market are almost the same using the principles to run. If the display shutdown after few seconds and the salve inverter board is still receiving 24 supply voltage then this mean the mainboard is working fine and the problem is in the inverter board.

There are few possibilities why the display shutdown:

1) one of the backlights is already weak/burnt

2) one of the transformers is bad. You can compare the primary and secondary windings ohm value between one transformer and with the others. If there is a different in the ohm reading then possibility that transformer have problem and it need to be replaced.

3) Surrounding/corresponding components that are located nearby the high voltage transformer have problem.

4) The inverter ic itself have problem.

Here is a tip that you use to find out the fault:

http://www.bestelectronicarticles.com/consumer-electronics/lcd-televisions/how-to-bypass-lcd-tv-inverter-board-shutdown-backlight-system.html

Hope this helps and would like to get to know  your update on this repair.

Jestine
http://www.JestineYong.com

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Hi Jestine

The startup resistor in a SMPS circuit seems to confuse me.

The colour of resistor is light blue.The color code are red (it seems to be more maroon), blue, green and silver which according to internet resistor calculators add up to 2.6 megaohms.

However when I use my multimeter it measures 1.005 m. Is this resistor different to other resistors. I noticed 2 of these resistors.

According to ohms law 220v resistance 2.6m ,my amps work out to 84a to supply oscillation circuit

Does it sound right. FYI I have not done any replacement parts yet as I am still getting familiar with how SMPS works.

I am about to order parts.

Thank you

Gasant

HI Gasant,

Resistor value usually will go up or open circuit and not going down. If you get 1 meg this mean the resistor color should be brown, black, greena and silver/gold. Try get another friend to check out on the colors. Sometimes  if a resistor went through heat for certain amount of time will cause the color to change slightly. For example a yellow color can turn into orange color.

Jestine

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hello sir,
thanks to your technical support, i want some information about EHT (extra high tension) part in t.v. last time i had a problem with my t.v when i was start it their is some sparking in picture tube. i want to know what is the exact problem in it.
thank & regaurds,
yogesh.

Sparking means either the pctube or the flyback have problem. If the high voltage is too high the picture tube will spark.

Jestine

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Could you suggest a good low cost Oscilloscope. A desk top woud be best.  I live in the US and it has been a long time sense I’ve work with one, about 30 years. What specs should I look for and a good brand.

Thanks

Larry

HI Larry,

You should get an analog or digital scope that have at least 100mhz so that you do not need to upgrade again. One of my ERG members bought this scope and found it to be very good.

http://www.ebay.com/itm/ATTEN-ADS1102CAL-100MHz-Digital-Oscilloscope-1102CAL-/320611527229

Jestine

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Hello Dear & Respected Sir,

I hope that u r enjoying GOD blessings.

A 15″ monitor was brought to me in dead condition. after checking it was found that main FET (K2333), a zenor diode value (18V), current sense resistor (.22 ohms),a resistor (470ohms) in SMPS and HOT were shorted and open as well.

All components replaced accordingly. But at the time of power ON, capacitors on secondary side of SMPS blast and output voltage level is too high rather than actual level.

I re-checked all components including newly replaced. But nothing found.

Kindly help.

With best regards

Daud Asi

HI Daud,

Check the resistors nearby the optoisolator ic secondary side. If one of the resistor open circuit the output voltages will increase.

Jestine

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Compliments of the new season.

Im having a problem testing a digital transistor  TC124E. its supposed to have a resisitor on its base. i measured across B-E and B-C but could not get anything.

Which other transistors can i use as its equivalent since i can not get it in our Electronic shops.

William

Hi William,

From my databook the suggested part numbers are:

AA1F4M, RN1003, UN4212 and 2SC3400

Jestine
http://www.JestineYong.com

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Hello Jestine, I will like to know from you if you know the best country in the world that used lcd monitors can be gotten at the cheapest price.My purpose of asking you this question is because I am aspiring to be importing lcd monitors,repairing and reselling to the public.

So kindly explain to me the easiest way you think i can achieved this purpose in some years to come.

Thanks

Hi Victor,

As far as i know nowadays all lcd monitors are made in China thus you should search for the china website that sell this item. Please be aware that there are lots of conmen out there and they could cheat your money without send you the item. You need to fly over to China to meet them and make sure they have factory .

Jestine

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HI Boling,

The B+ FET gate signal is about 9Vpp with either 640×480 or 800×600, as you could see at the photo attached. Is the gate signal Vpp the same with different resolution? Could you make any conclusion with this hint, why is the display blank with higher resolution?

By right different resolution the peak voltage will change. Sorry i have forgotten that CPU and eeprom also plays an important role about resolution. If you have any crt monitor schematic you could see the cpu have the CS pins (ie cs1, cs 2 cs3 and etc) This cs pin is use to trigger the fet in the s-correction circuit. If there is a problem with cpu or eeprom data corrupted the cs signal may not be accurate or missing thus eventually could cause no display symptom.

 

About LG CRT with problem of relay pulsating with no picture, what are the best points to measure all the output voltages from the smps?

Make sure the smps output stable voltages then check CPU make sure have stable 5 volt. The relay signal is coming from cpu. You can trace  from the relay driver transistor the base signal is from the cpu. if this signal is on and off then chances the cpu or the eeprom have problem.

About another CRT monitor with led became amber after being switched on for a few seconds with or without signal, how could I know the pins of the h/v signal at the cpu IC, since most cpu ICs don’t have any marks at its bottom?

You can trace from the vga signal cable.The two lines from the vga connector will surely go to the cpu pin perhaps they could pass thru one or two components before reaching the cpu pins.

From your experience, do I have to directly replace the power IC if the power FET is blown, since sometimes they are still OK, checked with power IC tester?

Usually if power fet blown the power ic will blow too. The ic checker is not 100% accurate as the best tester is still the monitor power supply itself.

Can I replace UC3842 with UC3842AN, KA3842A or KA3842B?

Most of the power supplies will support it. However to some, it will cause very faint horizontal lines across the screen especially white screen

Still another old Samsung Syncmaster 450b 15″ CRT monitor with the problem of very little width adjustment and pin cushion problem. After I power it on for a few minutes, there is a burst sound but without any smoke or any noticeable burnt component. What is the problem?

I suggest that you recheck the modulation and the pincushion transistor and surrounding circuit. Try recheck where the source from. There must be a reason why there was sound.

Have a great weekend and best wishes for the chinese new year,

Thanks and wishing you Chinese New Year.

Jestine

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By the way, could I ask you
a general question for trouble shooing the LCD monitor not turning on
problem. I face this problem a few times before but I really don’t know what
is the causes. I measure the low voltage side of the power board and find
the voltage is not stable but fluctuating up and down slowly for a few volts
at about 1Hz. All the capacitors seems to be in good conditions. What is
the most possible reason for that?

You are greatly appreciated If you can give me some suggestions.

Thanks

Ricky

HI Ricky,

Thanks for the egreeting card. Out voltages not stable could be due to the power supply itself or the inverter/mainboard have component shorted. Try remove the pico fuse and see if the power supply still fluctutate. if it still fluctuate then most likely you have to check all the components in the power side. if all check to be good then you need to direct replace the power ic and retest.

Jestine

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Jestine,

I shave not been able to fix the TV yet, but upon closer observation, I realised that it is one of the inverter boards at fault. With all the CCFLs plugged in the TV flashes for a second and turns off. However, if you connect the tubes 1 pair at a time (each connector fires two tubes), it displays the same behaviour, except for connectors 5 and 6. When you connect these, it turns off almost instantly, which makes me believe its something about tthe feedback. I looked at the CCFLs, they all look the same no black spots etc.

Binto

Hi Binto,

Try this link:

http://www.bestelectronicarticles.com/consumer-electronics/lcd-televisions/how-to-bypass-lcd-tv-inverter-board-shutdown-backlight-system.html?replytocom=57

Jestine
http://www.JestineYong.com

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